Alternating-current motor.



- PATENTED MAR. 24, 1903.

I A. w. SOHRAMM. ALTERNATING CURRENT MOTOR. APPLICATION FILED JULY 26,1902.

'50 MODEL.

[M565 I v I UNITED STATES PATENT OFFICE.

ADOLPH \V. SOIIRAMM, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR OF ONE-HALFTO EDIVARD B. VVILFORD, OF PHILADELPHIA, PENNSYL- VANIA.

ALTERNATlNG-CURRENT MOTOR.

SPECIFICATION forming part of Letters Patent N 0. 723,786, dated March24, 1903. Application filed July 26, 1902. Serial No. 117,12 1. (Nomodel.)

To ttZZ whmn it may concern:

Be it known that I, ADOLPH WV. SOHRAMM, a citizen of the United States,residing in Philadelphia, Pennsylvania, have invented certainImprovements in Alternating-Current Motors, of which thefollowingisaspecification.

My invention consists in certain improvements in alternating-currentmotors of the single-phase type, the object of the in vention beingtoprovide a motor of such a design that in addition to having arelatively large starting torque it shall be efficient in operation andeasily reversible.

A further object of the invention is to provide a motor which shall havea high-power factor and which shall maintain a practically constantspeed under normal load variations at each position of the controller.

These objects I attain as hereinafter set forth, reference being had tothe accompanying drawings, in which Figure l is a view, partlyindiagram, showing an electric motorwith its necessary apparatus connectedso as to operate in the manner contemplated by my invention; and Fig. 2is a view showing the connections of the motor and its apparatus whollyin diagram.

In the above drawings, A represents the main framework of a motor havinga laminated magnet-frame A, provided with polepieces upon which arecarried field-coils a. The main framework has the ordinary bearings b,in which is carried a shaft 6', having upon it an armature B, providedwith windings and a commutatorb similar in construction to that employedin any of the wellknown forms of direct -current machines. Brushes b andb are supported on any desired form of brush-holder, as 11 and themachine is operated in connection with atransformer which is also of anyof the well-known forms adapted to this type of work.

As is indicated in the figures, one of the supply-mains, as D, isconnected to one end of the primary windings O of the transformer, whoseother end is connected to one of the field-magnet windings a, the secondsupplymain being connected to the remaining end of the saidfield-winding.

One brush or set of brushes, as U is connected to one end oft-hesecondary windings O of the transformer, and there is a series oftaps connecting various points of the said secondary winding tocontact-pieces c. The sec- 0nd brush or sets of brushes 1) of the motorare con nected to a movable contactarm, (represented at 0,) which is soplaced and constructed as to make contact with any one of thecontact-pieces c.

In order to reverse the direction of rotation of the motor, a switch clof any convenient design is provided, and this may be placed so as toreverse the armature connections, the connections to the primary windingof the transformer, or to the field connections,in which latter positionit is illustrated in Fig.

l of the drawings.

In operation single-phase current is supplied to the mains D and D, andthe arma- 7o ture B is caused to revolve in the Well-known manner, thespeed of revolution being varied by moving thearm 0 over the contacts 0,and thereby cutting into or out ofcircuit more or less of the secondarywindingO of the transformer.

When desired, the speed of the motor may be varied by varying theelectromotive force impressed upon the armature, this beingaccotnplished in any one of a number of ways as, for'example, bychanging the magnetic circuit of the transformer.

As shown in Fig. 2, I may, if I desire, arrange the secondary winding ofthe transformer so that when the movable contact-arm o is moved in onedirection from its central position the armature of the motor will turnin one direction, while if such arm be moved to the other side of thecentral position the direction of rotation of the armature will bereversed.

An important advantage of the method of connection and operation of myimproved motor will be seen when it is noted that the windings upon thearmature B and the windn ing of the secondary O are the same or bearconstant ratio to each other irrespective of the impressed voltage ofthe current supplied from the mains D and D. It is therefore possible towind the armature for motors of I00 the type above described, as well asthe secondaries of the transformers, with wire of the most suitable sizefrom commercial and mechanical stand points.

In order to change the power factor of the combination, 1 may connect'acondenser d in parallel either with the field-coil of the motor or withthe primary winding of the transformer. if considered advisable, anon-indnctive resistance d may be substituted for the condenser, Fig. 2illustrating the condenser as placed around the fields of the motor andthe resistance similarly placed in shunt to the primary of thetransformer.

It will of course be understood that the primary winding 0" of thetransformer and the field-coils of each motor have to be varied to suitthe voltage at which the motor is to be op-, erated, this, however,being a comparatively simple matter as long as the armature-winding andthe secondary of the transformer may be made the same for all voltages.It is further to be noted that the connections to the armature of themotor are not in any way electrically connected with the externalsupply-circuit or with the main supply-wires D and D, and it will beunderstood by those skilled in the art that the possibility of damage tothe armature and commutator from grounds is thus prevented. Theimportance of this feature will be appreciated when it is rememberedthat accidental grounds to one side of a suppy system are of veryfrequent, if not continual, occurrence. Occasion might arise, however,where in order to reduce the number of conductors connecting thetransformer-windings with the motor it would be advisable to use thewire connecting the pritnary of the transformer and field; also, forconnecting one side of the secondary to one of the armature-brushes.This would reduce the number of wires from the transformer to the tnotorfrom four to three, which would be advantageous in certain cases wherethe point of control is at a considerable distance from the motor.

As a result of the above-described connection of apparatus it is foundthat the power factor of my improved motor is high and may underconditions be made equal to unity. I have found in operation that thepower factor increases with the load up to certain limits and that thearmature-current is actually less for high than for a low load, sothateven if motion of the armature is entirely arrested which frequently areof vital importance.

I claim as my invention-- 1. The combination of an electric motor havingan armature of the direct-current type, with a transformer, thefield-coils of the motor being connected to the supply-mains in serieswith the primary winding of the transformer and the brushes or sets ofbrushes of the motor having means whereby they are connected to thesecondary winding of said transformer, said means includingcontactpieces connected at intervals to said secondary winding and anarm placed to operate upon said contact-pieces, said connections beingso made to the secondary winding that the armature will rotate inonedirection when said arm contacts with certain of the contactpiecesand will rotate in the opposite direction when the arm contacts withothers of said pieces, substantially as described.

2. The combination of an electric motor having an armature of thedirect-current type, with a transformer, the secondary winding of thetransformer having a series of contactpieces connected to it atintervals and one of the brushes or sets of brushes of the armaturebeing connected to the said secondary Winding at some point of itslength between certain of the connections of the contact-pieces thesecond armature brush or set of brushes having a device designed tocontact with any of the contact-points connected to the secondarywinding so as to cause rotation of the armatn re in one direction whenon certain of said contacts and in the opposite direction when engagingcertain others of the same, substantially as described.

3. The combination of a motor and a transfortner, one armature-terminalof said motor being connected to the secondary winding of thetransformer at a point thereon between its ends, a series ofcontact-pieces, connected to different points of said secondary winding,and a contact-piece connected to the second armature-terminal and placedto engage the contact-pieces on both sides of the point of theconnection of the first armature-terminal, substantially as described.

4. The combination of a motor and a transformer, said motor having itsfield-coils connected in series with the primary winding of thetransformer and connected to the supplymains, the secondary winding ofthe transformer beingin a closed circuitincluding the armature of themotor, with a reversingswitch connected in the circuit including thearmature, whereby the connection to the terminals of said armature maybe changed relatively to the terminals of the secondary winding of thetransformer, substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

AD OLPH W. SCHRAM M.

Witnesses:

WILLIAM E. BRADLEY, J 0s. H. KLEIN.

ICO

